1. Field of Invention
This application relates to computed tomography systems and more particularly to multi-detector computed tomography systems for combined myocardial perfusion imaging and the diagnosis of coronary artery disease.
2. Discussion of Related Art
The contents of all references, including articles, published patent applications and patents referred to anywhere in this specification are hereby incorporated by reference.
Multidetector computed tomography coronary angiography (MDCTA) provides non-invasive assessment of coronary atherosclerosis (Raff G L, Gallagher M J, O'Neill W W, et al. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol. Aug. 2 2005; 46(3):552-557; Leschka S, Alkadhi H, Plass A, et al. Accuracy of MSCT coronary angiography with 64-slice technology: first experience. Eur Heart J. August 2005; 26(15):1482-1487; Leber A W, Knez A, von Ziegler F, et al. Quantification of obstructive and nonobstructive coronary lesions by 64-slice computed tomography: a comparative study with quantitative coronary angiography and intravascular ultrasound. J Am Coll Cardiol. Jul. 5 2005; 46(1):147-154; Mollet N R, Cademartiri F, Nieman K, et al. Multislice spiral computed tomography coronary angiography in patients with stable angina pectoris. J Am Coll Cardiol. Jun. 16 2004; 43(12):2265-2270). However, a number of studies have demonstrated that coronary atherosclerosis measurements by MDCTA are not highly predictive of ischemia (Hacker M, Jakobs T, Matthiesen F, et al. Comparison of spiral multidetector CT angiography and myocardial perfusion imaging in the noninvasive detection of functionally relevant coronary artery lesions: first clinical experiences. J Nucl Med. August 2005; 46(8):1294-1300; Rispler S, Keidar Z, Ghersin E, et al. Integrated single-photon emission computed tomography and computed tomography coronary angiography for the assessment of hemodynamically significant coronary artery lesions. J Am Coll Cardiol. Mar. 13 2007; 49(10):1059-1067; Schuijf J D, Wijns W, Jukema J W, et al. Relationship between noninvasive coronary angiography with multi-slice computed tomography and myocardial perfusion imaging. J Am Coll Cardiol. Dec. 19 2006; 48(12):2508-2514). These observations have fueled the pursuit of hybrid imaging strategies that combine radionuclide myocardial perfusion imaging (MPI) with MDCTA. While promising, this approach is limited by higher radiation doses, imperfect co-registration of datasets, and the cost of hybrid imaging (Rispler S, Keidar Z, Ghersin E, et al. Integrated single-photon emission computed tomography and computed tomography coronary angiography for the assessment of hemodynamically significant coronary artery lesions. J Am Coll Cardiol. Mar. 13 2007; 49(10):1059-1067). Thus, it would be attractive if MDCT alone could provide both atherosclerosis and perfusion imaging in a single, self-registered exam.
However, accurate quantitative MPI using magnetic resonance or positron emission tomography (PET) rely heavily on the precise characterization of the arterial input function (AIF) or the arterial delivery of contrast/tracer to the myocardium (Christian T F, Rettmann D W, Aletras A H, et al. Absolute myocardial perfusion in canines measured by using dual-bolus first-pass MR imaging. Radiology. September 2004; 232(3):677-684; Jerosch-Herold M, Wilke N, Stillman AE. Magnetic resonance quantification of the myocardial perfusion reserve with a Fermi function model for constrained deconvolution. Med Phys. January 1998; 25(1):73-84; Schelbert H R, Phelps M E, Huang S C, et al. N-13 ammonia as an indicator of myocardial blood flow. Circulation. June 1981; 63(6):1259-1272). Likewise, previous studies using X-ray computed tomography have incorporated the AIF into the quantification of myocardial blood flow (MBF), but required dynamic CT imaging of the heart (Mohlenkamp S, Behrenbeck T R, Lerman A, et al. Coronary microvascular functional reserve: quantification of long-term changes with electron-beam CT preliminary results in a porcine model. Radiology. October 2001; 221(1):229-236; Rumberger J A, Feiring A J, Lipton M J, et al. Use of ultrafast computed tomography to quantitate regional myocardial perfusion: a preliminary report. J Am Coll Cardiol. January 1987; 9(1):59-69; Wang T W X, Chung N, et al. Myocardial Blood Flow Estimated by Synchronous Multislice, High-Speed Computed Tomography. IEEE Trans. Med. Imaging. 1989 1989; 8:70-77; Wolfkiel C J, Ferguson J L, Chomka E V, et al. Measurement of myocardial blood flow by ultrafast computed tomography. Circulation. December 1987; 76(6):1262-1273; Wu X S, Ewert D L, Liu Y H, et al. In vivo relation of intramyocardial blood volume to myocardial perfusion. Evidence supporting microvascular site for autoregulation. Circulation. February 1992; 85(2):730-737). Together, these studies further illustrate that the accurate characterization of the AIF is essential to quantitative MPI.
Helical MDCT, unlike dynamic MDCT, acquires cardiac images over a short period of time (5-10 seconds) during peak contrast enhancement using a spiral mode of scanning. Due to the spiral nature of MDCTA acquisition, it is generally thought that information regarding contrast kinetics, such as the AIF, cannot be obtained. Interestingly, MDCTA imaging protocols actually do acquire image data that can be used to reconstruct the AIF according to embodiments of the current invention. Many MDCTA protocols use an automated bolus tracking method for triggering the appropriate time for helical MDCT scanning of the coronary arteries. Bolus tracking image data records the early part of contrast enhancement over time, data that is usually discarded following imaging. Additionally, helical MDCT images can be registered to the time of acquisition and can be used to construct the latter portion of the AIF according to embodiments of the current invention. Therefore, by combining the dynamic bolus tracking and time-registered helical MDCT image data sets, the time-attenuation curve of the AIF can be constructed according to embodiments of the current invention. There is thus a need for improved multi-detector computed tomography systems for combined myocardial perfusion imaging and the diagnosis of coronary artery disease.